A Multifunctional "Halide-Equivalent" Anion Enabling Efficient CsPb(Br/I) 3 Nanocrystals Pure-Red Light-Emitting Diodes with External Quantum Efficiency Exceeding 23.

Pure-red perovskite LEDs (PeLEDs) based on CsPb(Br/I) nanocrystals (NCs) usually suffer from a compromise in emission efficiency and spectral stability on account of the surface halide vacancies-induced nonradiative recombination loss, halide phase segregation, and self-doping effect. Herein, a "halide-equivalent" anion of benzenesulfonate (BS ) is introduced into CsPb(Br/I) NCs as multifunctional additive to simultaneously address the above challenging issues. Joint experiment-theory characterizations reveal that the BS can not only passivate the uncoordinated Pb -related defects at the surface of NCs, but also increase the formation energy of halide vacancies. Moreover, because of the strong electron-withdrawing property of sulfonate group, electrons are expected to transfer from the CsPb(Br/I) NC to BS for reducing the self-doping effect and altering the n-type behavior of CsPb(Br/I) NCs to near ambipolarity. Eventually, synergistic boost in device performance is achieved for pure-red PeLEDs with CIE coordinates of (0.70, 0.30) and a champion external quantum efficiency of 23.5%, which is one of the best value among the ever-reported red PeLEDs approaching to the Rec. 2020 red primary color. Moreover, the BS -modified PeLED exhibits negligible wavelength shift under different operating voltages. This strategy paves an efficient way for improving the efficiency and stability of pure-red PeLEDs.